Tandem,free-piston machines



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f/enr i3/d6 ATTORNEYS March 17, 1970 H. BENAROYA 3,501,087

TANDEM, FREE-PISTON MACHINES Filed May 20, 1968 y 4 Sheets-Sheet 2 INVENTOR A/en/'y @amsn-ayaV ATTORNEYS March 17, 1970 H, BENAROYA 3,501,087

TANDEM, FREE-PISTON MACHINES Filed May 20, 1968 4 Sheets-Sheet :5

INVENTOR Henry en a roya March 17, 1970 H. BENAROYA TANDEM, FREE-PISTON MACHINES Filed May 20, 1968 4 Sheets-Sheet 4 m n m INVENTOR Hem-)1 en a raya MIM/2% ATTORNEYS United States Patent 3,501,087 TANDEM, FREE-PISTON MACHINES Henry Benaroya, 41 Boulevard du Commandant Charcot, 92 Neuilly-sur-Seine, France Filed May 20, 1968, Ser. No. 730,290 Claims priority, applicatior6i France, May 24, 1967,

101, s Int. cl. Fozb 71 /06, F041 31/00 U.S. Cl. 230-56 17 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to tandem, free-piston machines, that is to say to machines comprising two aligned drive cylinders in each of which work two opposed free drive pistons.

The neighbouring inner drive pistons are mechanically connected to each other and form a rst group, whereas the two outer pistons are also mechanically connected to each other and form a second group, the mechanical connection means of this latter group comprising at least one rod which is parallel to the axis of the machine and passes at the exterior of the drive cylinders, this rod being ydesignated hereafter by the expression conjugation rod, it being understood that this term covers all the variants of rods or of analogous elements lling the same function.

These two groups of drive pistons are connected by synchronization means so that -when the two opposed movement drive pistons that work in one of these drive cylinders perform their work stroke, the two opposed movement pistons that work in the other cylinder perform their compression stroke, and vice-versa.

The energy released by the combustion of fuel in the drive cylinders generally serves for compressing air which can be used outside the free-piston machine, which then forms a motor compressor, or which can be used at the interior of the free-piston machine to supercharge and scavenge the drive cylinders of this machine and to form `with the incompletely expanded combustion gases a mixture of hot gas under pressure which, after its exhaust from the exhaust ports of the drive cylinders, serves for driving a receptive machine, notably a turbine, the machines of this latter type thus working as gas generators.

Of course, the same machine can furnish a hot gas under pressure to a receptive machine and pure compressed air to another receiver at the same time.

The conjugation rods of the second group of drive pistons are generally long and are as a rule intended solely to work under traction stress. Nevertheless, in the tandem, opposed free-piston machines of the type in question, the conjugation rods can, however, `be subjected at certain times, to compression stresses. This disadvantage could be palliated by increasing the crosssection of these rods, but this would lead to a greater weight of the machine and to a disadvantageous increase of the forces of inertia.

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The chief object of the present invention is to remedy these disadvantages and to arrange these machines so that the conjugation rod or rods work solely in traction along the totality of the strokes of the drive pistons of the tandem machine.

Furthermore, an object of the invention is to reduce the cumbersomeness of the machine, notably in the axial sense.

The tandem, free-piston machine according to the present invention is characterized in that each of the outer pistons, that is to say each of the pistons of the second group, is connected to a compensator piston working preferably as an air compressor piston which creates, in a compensator cylinder, a resistance to the movement during the inward stroke of the corresponding drive piston, that is to say while the compression takes place in the drive cylinder in which this drive piston works.

The compensator pistons and their cylinders can form separate compensation units which are located at the ends of the machine, but they can also be united in a single unit, in which the piston works as a double acting piston in a single compensator cylinder, this double acting piston being preferably inserted in a conjugation rod. In all cases, the resistance to which the compensator piston is subjected during the inward movement of the corresponding drive piston, is thus added to the resistance to which this latter piston is subjected, due to the compression of the air at the interior of the drive cylinder.

According to a preferred embodiment of the invention, there is inserted in the mechanical connection of the Irst group of drive pistons, which connection is generally formed by a single rod, a compressor piston which works as a double acting piston in a compressor cylinder which is located between the two drive cylinders. In this manner, a particularly compact machine is obtained exempt from compression stress in the conjugation rods.

When the compensator pistons working as single acting air compressor pistons and the corresponding compensator cylinders are disposed, in a gas generator constructed according to the preceding paragraph, at the opposite ends of this machine, the compensator cylinder and the compression space (of the compressor cylinder), which is located on the same side of the double acting compressor piston as this compensator cylinder, are arranged to communicate with the inlet ports of the drive cylinder which is disposed, with respect to the center of the tandem machine, on the side opposite to the side where this compensator cylinder and compressor space are located. The result is that each drive cylinder is supplied by two compressor spaces which are'located at different distances from the drive cylinder that they supply, which permits continuous scavenging of each of the drive cylinders during practically the entire duration that the inlet ports of these cylinders are open.

Several embodiments of the invention, given merely by way of example, are represented in the accompanying drawings, in which: v

FIGURE l is a schematic representation of a first embodiment of a tandem, free-piston machine according to the invention;

FIGURE 2 is a section through a second embodiment of a tandem machine according to the invention;

FIGURE 3 is a schematic representation in section of still another embodiment of such a tandem machine;

FIGURE 4 is a sectional view along IV-IV of FIG- URE 3;

FIGURE 5 represents a section through an outer drive piston associated with a compensator piston-cylinder ensemble according to a particular embodiment of these elements; and

FIGURE 6 shows, in axial section, still another embodiment of the invention.

First of all, with regard to the tandem, free-piston machine in its overall aspect, with the exception of its compressor elements and the means forming the subject matter of the present invention, this machine comprises, in a manner known in itself, a tirst and a second drive cylinder 11 and 12, coaxial with each other, in each of which two drive pistons 21, 31 and 22, 32 (FIGURES 1 to 3) work in phase opposition. The inner pistons 21 and 22 forming a first group are interconnected by a rigid connection rod 4 and the outer pistons 31 and 32 forming a second group are interconnected, also in a rigid manner, by an ensemble of elements comprising rods 61 and 62 directly lixed to these pistons and terminated by members 71 and 72, in their turn interconnected by conjugation rods 8 passing at the exterior of the drive cylinders 11 and 12.

In this manner two systems having inverse displacements are obtained, whose movements can be synchronized in a manner known in itself, as shown schematically in FIGURES 2 and 3, by the intermediary of racks 91 and 92 respectively rigid with these two systems and meshing with a common pinion 11.

The distribution of the drive cylinders is assured by the intermediary, on the one hand, of inlet ports 121, 122 formed in these drive cylinders and adapted to put the drive cylinders in communication with reservoirs or casings 131, 132 containing scavenging air delivered into these casings by compressor elements (of which several advantageous embodiments will be described hereafter), and, on the other hand, exhaust ports 141, 142 permitting the exhaust of a mixture of air and combustion products, for example towards a receptive turbine (not shown) through conduits 151, 152 when these ports are cleared by the corresponding drive pistons, during the last portions of their strokes towards their respective outer dead points.

According to the present invention, in the embodiment represented in FIGURE 1, each of the outer drive pistons 31, 32 is rigidly associated with a compressor piston, called compensator piston, 161 and 162, each of these compensator pistons working as a single acting piston in a compensator cylinder 171 or 172. Each of the pistons 161 and 162 compresses air in the corresponding compensator cylinder when the drive piston with which it is associated compresses the combustion air in its drive cylinder.

The adjunction of this compensator piston-cylinder ensemble to each of the outer drive pistons tends to brake the one of these drive pistons which performs its inward stroke, and, accordingly, constantly maintains the conjugation rods `8 under tension, or in other words, assures that these rods work solely in traction along the totality of their strokes.

As already mentioned, the ensemble formed by each of the compensator pistons 161 and 162 and its corresponding compensator cylinder forms a single acting compressor element communicating with the reservoir 131 (or 132) of scavenging air for the drive cylinder 11 (or 12) and coacting with the corresponding drive piston, the tandem machine thus formed then comprising such a compressor element at each of its ends. In addition to these two single acting compressor elements, respectively rigid with the outer drive pistons, the machine advantageously further comprises a double acting central compressor element whose cylinder 18 is disposed between the drive cylinders 11 and 12 and whose piston element 19 is rigidly inserted in the connection 4 of the inner drive pistons 21 and 22.

The distribution of these compressor elements is arranged in a manner known in itself, the cylinders 171, 172 comprising on the inner side of the pistons 161, 162 air inlet valves 211, 212 respectively; delivery valves 221, 222 permit the casings 131, 132 to be supplied with air during the respective delivery strokes of the single acting compressor pistons 161, 162. Similarly, the double acting compressor cylinder 18 comprises, respectively in one and the other of the two compartments dened in the cylinder 18 by the piston 19, inlet valves 231 and 232 and valves 241 and 242, these latter valves assuring the delivery of the compressed air alternately into one and the other of the casing 131 and 132 of the machine (as represented in FIGURE 1), or into a reservoir 25 (of the type represented in FIGURE 2) maintaining a constant communication between these two casings.

FIGURE 2, in which the elements that are equivalent to those of the machine already described are designated by the same reference characters, represents another' embodiment of the invention.

According to this figure, the machine comprises, on the one hand, a first compressor element comprising a compressor cylinder 261 in which works a double acting compressor piston 271, inserted in the rigid connection 4 between the two inner drive pistons 21, 22, and on the other hand, a second compressor element playing the role of the compensator element and comprising at least one compressor cylinder 262 in which works at least one second double acting compressor piston 272 inserted in the conjugation rods 8 of the outer drive pistons 31, 32.

In this embodiment, the first and second compressor elements mentioned above are coaxial and are both disposed between the two drive cylinders of the machine, the rigid conrection 4 between the two inner drive pistons 21, 22 passing through the piston 272 of the second compressor element, and the conjugation rods 8 'passing through the piston 271 of the lirst compressor element mentioned above.

In this embodiment of a tandem, free-piston machine according to the invention, there are furthermore advantageously provided means for assuring the tightness between the two compressor cylinders 261 and 262.

For this purpose, in the cylinder 261, the two ends 2812`- and 2811, are interconnected by hollow stay-rods 29 at the interior of which slide the conjugation rods 8, and similarly, in the compressor cylinder 262, the tow ends 282 and 2821, are interconnected by a single hollow stay-rod 31 in which slides the connection rod 4.

With regard to the tightness between the two adjacent compression chambers defined by the compressor piston in each of the above mentioned double acting compression elements, it can be assured, in a manner known in itself, for example, by the intermediary, on the one hand, of exterior piston rings 321, 322 on the exterior parts of the pistons 271, 272 making frictional contact with the interior walls of the cylinders 261 and 262, and on the other hand, interior piston rings 33, 314 making frictional contact with the respective exterior walls of the fixed staytubes 29 and 31.

In addition to the tightness thus achieved between the various compression chambers, the supplementary advantage is also obtained that the relative speeds of the movable frictional pieces with respect to the fixed pieces does not exceed the speed of each of the systems, whereas the relative speed of the pistons with respect to the rods that pass through them is twice the speed of displacement of the pistons.

In this manner a tandem machine is obtained of reduced size in which the compressor and compensator elements are formed in a compact block at the center of the machine.

A supplementary advantage of this feature resides in the facility of assembling and dismantling the machine, and in particular, in the preferred case in which the outer drive piston-s co-operate with the exhaust ports of the drive cylinders, the easy possibility of dismantling and of upkeep or replacement of these latter pistons, which are always subject to the most thermal stress during operation of the tandem machine.

Needless t0 say, in the machine represented in FIGURE 2, the partitions 2811, and 282,1 could be eliminated so that two compressor elements would be obtained each comprising a compressor piston coacting with a common compressor cylinder and defining in this cylinder three compression chambers of variable volume. Of course, in such a case, the hollow rods of the type identified previously by the reference numerals `29 and 31 could no longer be used, the compressor pistons 271, 272 then sliding directly respectively on the rods 8 and the connection rod 4.

The problem of the compressor pistons sliding on rods is nevertheless eliminated in the embodiment of the machine represented in FIGURE 3 in which only the one of the compressor elements whose piston is inserted in the connection 4 of the inner drive pistons 21, 22 is disposed between the corresponding drive cylinders, whereas the cylinder or cylinders of the compensator element that is rigid with the outer drive pistons 31, 32 is disposed along an axis or axes parallel to the axis of the drive pistons, these axes :being themselves disposed at the exterior of the largest cylindrical volume of the ensemble forming the machine.

According to a particularly advantageous mode of construction of the invention, the compensator element forming the second compressor element comprises a plurality of compressor cylinders, for example three compressor cylinders 2621 2621 262c disposed at the vertexes of an equilateral triangle whose center coincides with the axis of the rst compressor element 261, 271 as shown in FIGURE 4, these three compressor cylinders coacting with three pistons mounted in three rods y82, 81 82.

Of course the cross-sections of the cylinders 2622, 2621J 262c are considerably smaller than the cross-section of the compressor cylinder 261 in a ratio substantially equal to 1/ 3 when these cylinders 262,1, 2621 2621, coact with single pistons, so that the volumes of air delivered by the two compressor groups into the casings 131, 132 remain substantially equal.

The diameters of the cylinders 2622, 2621 262C can be further reduced if they are divided into a plurality of chambers, for example two chambers 362, 3161 coaxial and disposed end to end, these chambers coacting with single acting compressor .piston elements 372, 371, inserted at a distance one from the other in the above mentioned rods. The respective cross-sections of the cylinders 2622, 2621 262c will, in this case, only be of the order of 1/6 of that of the cylinder 261.

The rods 8, coupled to the members 71, 72 form the connection rods of the multiple pistons such as 37a, 37b which coact with the exterior compressor cylinders 362, 361,.

A construction is thus obtained which is perhaps even more advantageous in certain respects than in the case of FIGURE 2, in particular with regard to the elimination of friction along the compressor pistons and the movable rods, and the increased compactness of the overall machine.

The pistons 37a, 371, forming the compensator pistons only wor-k as single acting pistons by their faces that face each other, in the manner of the pistons 161, 162 of FIGURE l.

An embodiment will now =be described of one of these compensator piston-cylinder ensembles such as provided in FIGURE l, in relation'to the drive piston 32, it being understood that the other drive piston 3=1 is provided with an equivalent ensemble.

The compensator piston of the ensemble in question is formed, as shown in FIGURE 5, by a piston element 162, rigid with the outer drive piston 32, and of cross-section a little greater, this piston coacting with a cylinder element 172 communicating with the casing 132, surrounding the drive cylinder 12, by one or more openings 38 in which delivery valves (not shown in FIGURE 5) can be established if appropriate, analogous to the valves 222 of FIGURE 1.

In such a case, the ensemble of the compensator piston 1162 and the compensator cylinder 172 forms a veritable auxiliary, single acting compressor element.

As for the gas generator according to the invention, shown in FIGURE `6, it corresponds to the machine of FIGURE 1 with regard to the general disposition of the drive and compressor cylinders, as well as to the connections between the various free pistons.

The air compressed by the outer compensator pistons 1061, 1062 serves, with the air compressed by the double acting piston 104, for supplying the drive cylinders 1011, 1012.

In the machine represented in FIGURE 6, the compressor spaces that are located on one side of the center of the tendem machine communicate with the inlet ports of the drive cylinder that is located on the other side of the center of the tendem machine. Thus the compressor space 1071 and the compressor space which is located in the compressor cylinder of the left hand side of the compressor piston 104 supply in common the drive cylinder 1012 that is located on the right hand side of the machine. The communication of these two compressor spaces with the inlet ports 1122 of the drive cylinder 1012 is assured by conduits 1501 and 1502 of dierent length. In an analogous manner, the drive cylinder 1011 is supplied by the air compressed in the compressor space 1072 and in the compressor spacethat is located on the right hand side of the compressor piston 104. For this purpose, these latter compressor spaces communicate lwith the inlet ports 1121 of the cylinder 1011 by the intermediary of conduits 1511 and 1512.

In this manner, not only do the delivery periods of the compressor pistons that deliver the air towards the inlet ports of one of the drive cylinders coincide with the periods during which the inlet ports of this cylinder are open, but also the supply of combustion air and scavenging air to each of the drive cylinders lasts for practically the entire duration that these ports are open; this is due to the ditferent lengths of the conduits 1501, 1502 and 1511, 1512, these differences of the lengths delaying the arrival at the corresponding drive cylinder of the air compressed by the outer compressor pistons with respect to the arrival of the air compressed by the inner, double acting compressor piston 104.

In the case in which the compressed air, before its entry into the .drive cylinders, should undergo cooling, cooling means 1521, 1522 and 1531, 1532 can be inserted in the various conduits 1501, 1502, 1511 and 1512. The cooling eiects of these cooling means can be different. Thus, more effective cooling means can be provided in the conduits 1502 and 1512 than in the conduits 1501 and 1511 in order to accentuate the cooling of the air at the beginning of the scavenging with respect to the cooling of the air that assures the end of the scavenging.

Many changes and modifications can be made without departing from the spirit and scope of the present invention. For example, at least a part of the air compressed in at least certain of the compressor spaces of the tendem machine can be delivered towards the exterior without passing through the drive cylinders of the machine. In view of the extensive possibilities of changes and modications, the invention should not be limited to the particular embodiments described hereinbefore by way of example.

What I claim is:

1. A tandem, free-piston machine comprising:

two aligned drive cylinders each provided with inlet means and outlet means,

two opposed free drive pistons, namely an inner and an outer drive piston, disposed and adapted to work in one of said drive cylinders,

two opposed free drive pistons, namely an inner and an outer drive piston, disposed and adapted to work in the other of said drive cylinders,

inner mechanical connection means mechanically interconnecting said two inner drive pistons, whereby said two inner drive pistons form an inner group,

outer mechanical connection means mechanically interconnecting said two outer drive pistons, whereby said two outer drive pistons form an outer group, said outer mechanical connection means comprising at least one conjugation rod that is parallel to the axis of said drive cylinders and that passes at the exterior of said drive cylinders, synchronization means provided between Said two groups for synchronizing the movements of said drive pistons so that when said two opposed drive pistons in one of the drive cylinders perform their work strokes away from each other, said two opposed drive pistons in the other drive cylinder perform their compression strokes towards each other, and vice versa,

first compressor piston means connected to said inner group, and first compressor cylinder means in which work said first compressor piston means, and

second compressor piston means connected to said outer group, this connection including said conjugation rod, second compressor cylinder means in which work said second compressor piston means so a to form two compressor spaces in said second compressor cylinder means, the arrangement of said second compressor piston and cylinder means being such that each time that one of the drive pistons of said outer group performs its work stroke it drives not only the other drive piston of the outer group to perform its compression stroke but drives also by the intermediary of at least a part of the conjugation rod the second compressor piston means in such a manner that only in the compressor space turned toward the working drive piston with respect to said second compressor piston means air is compressed and expulsed whereas in the other compressor space air is sucked in.

2. A machine according to claim 1, wherein said first compressor piston and cylinder means is double acting and is disposed between said two drive cylinders, and comprises a double acting first compressor piston disposed in a first compressor cylinder and dividing said first compressor cylinder into two rst compressor compartments, one of which is located on one side of said double acting first compressor piston and the other of which is located on the other side of said double acting first compressor piston, said double acting first compressor piston being iixed to said inner mechanical connection means.

3. A machine according to claim 2, wherein there is only a single second compressor piston and cylinder means, which is common to said two outer drive pistons and comprises a single, double acting second compressor piston disposed in a single second compressor cylinder and dividing said single second compressor cylinder into two compartments, one of which is located on one side of said single second compressor piston and the other of which is located on the other side of said single second compressor piston.

4. A machine according to claim 2, wherein said second compressor piston and cylinder means comprises at least one second compressor piston which is mounted on a conjugation rod and works in a second compressor cylinder whose axis is laterally offset from the axis of said drive cylinders.

5. A machine according to claim 2, wherein said second compressor piston and cylinder means comprise two units, one disposed at each end of the machine, each said unit comprising a single acting second compressor piston disposed in a corresponding second compressor cylinder.

6. A machine according to claim 3, wherein said double acting second compressor piston and cylinder are disposed between said two drive cylinders, said second compressor piston being iixed to a conjugation rod which passes at the exterior of said drive cylinders.

7. A machine according to claim 6, wherein said double acting first compressor piston and cylinder and Said double acting second compressor piston and cylinder are disposed side by side between said two drive cylinders.

8. A machine according to claim 4, wherein said outer drive pistons are directlythat is to say, without the interposition of a compressor space-connected to said outer mechanical connection means, said outlet means of said drive cylinders are in the form of outlet ports, and said outer drive piston control the outlet ports of their corresponding drive cylinders.

9. A machine according to claim 7, wherein said at least one conjugation rod passes through said first compressor cylinder, at the interior of at least one tube which extends between the ends of said first compressor cylinder.

10. A machine according to claim 7, wherein said inner mechanical connection means passes through said second compressor cylinder, at the interior of a tube which extends between the ends of said second compressor cylinder.

11. A machine according to claim 9, wherein said inner mechanical connection means passes through said second compressor cylinder, at the interior of a tube which extends lbetween the ends of said second compressor cylinder.

12. A machine according to claim 4, `wherein there are a plurality of second compressor pistons and cylinders regularly distributed about the axis of said drive cylinders, said second compressor pistons being mounted respectively on a corresponding number of conjugation rods.

13. A machine according to claim 12, wherein said conjugation rods pass through the vertexes of an equilateral triangle lying in a plane at right angles to the axis of said drive cylinders.

14. A machine according to claim 5, wherein said inlet means of said drive cylinders are in the form of inlet ports, and a reservoir is provided in communication with said inlet ports, said second compressor piston and cylinder units lbeing adapted to deliver the air that they compress into said reservoir, whereby said air serves, in said drive cylinders, as scavenging air and as combustion air.

15. A machine according to claim 14, wherein the second compressor cylinder and the compressor compartment of the first compressor cylinder that is located, with respect to the double acting first compressor piston, on the same side as said second compressor cylinder, communicate via conduit means with the inlet ports of the drive cylinder that is disposed, -with respect to said double acting first compressor piston, on the side opposite to the side where the second compressor cylinder and the compressor compartment that assure its supply are located.

16. A machine according to claim 15, wherein cooling means are disposed in the conduit means that connect respectively each second compressor cylinder and each compressor compartment of the first compressor cylinder to the inlet ports of the opposite drive cylinder.

17. A machine according to claim 15, wherein the cooling means disposed in the conduit means connecting each compressor compartment of the first compressor cylinder to the inlet ports of the opposite drive cylinder are more effective than the cooling means disposed in the conduit means connecting each second compressor cylinder to the inlet ports of the opposite drive cylinder.

References Cited UNITED STATES PATENTS 2,027,877 1/1936 Pescara 230--56 3,347,215 10/1967 Pescara 230-56 FOREIGN PATENTS 316,032 8/1932 Italy.

ROBERT M. WALKER, Primary Examiner 

